Respirator hoods and helmets are well known and have many uses. For example, the hoods may be used to allow the user to breathe safely in a contaminated atmosphere, such as a smoke filled atmosphere, in a fire or a dust laden atmosphere, in a mine or a toxic atmosphere, or in a laboratory.
Respirator hoods and helmets also may be worn where it is desired to prevent the user from contaminating the surrounding atmosphere, such as when working in a clean room used to manufacture silicon chips.
Respirator helmets have a hard shell that provides head protection against impacts when working in a dangerous environment where the user is at risk of being struck by falling debris such as in a mine or on a building site.
Respirator hoods can be used where head protection is not required, for example, when working in a laboratory or a clean room. In such situations, the hoods are usually made of soft, flexible material for comfort and lightness.
The present invention has particular application to respirator hoods and in the following description and claims the term “hood” is used to mean “a loose fitting face piece that covers at least the face of the user but does not provide head protection” and is to be construed accordingly. It will be understood, however, that the invention is not limited to respirator hoods and, where the context permits, has application to both respirator hoods and respirator helmets.
One type of known respirator hood has a top wall and a side wall extending from the perimeter of the top wall in which the head of the user is received so as to enclose the head. Hoods of this type are commonly used with a body suit to isolate the user from the environment in which they are working.
The top wall and side wall are usually made of a soft material suitable for the environment in which the hood is to be worn and an apron or skirt may be provided at the lower end of the side wall that extends over the shoulder region of the user and covers the interface with the body suit.
The hood has a transparent region at the front, commonly referred to as a visor, through which the user can see. The visor may be an integral part of the hood or detachable so that it can be removed and replaced if damaged. The visor may extend to the sides of the hood and/or over the top of the hood to provide substantially unrestricted vision.
Examples of this type of hood are disclosed in UK Patent No. 1343132 and U.S. Pat. No. 4,458,680. In both these patents, the hood is provided with an air duct extending around the perimeter of the top wall on the inside of the hood. The duct is connected to an incoming air supply pipe that passes through the inside of the hood behind the head of the user and has an array of outlet holes arranged to direct air down towards the user's face.
The air supply pipe may be connected to a remote air source separate from the user, but for many applications the air supply pipe is connected to a portable air source carried by the user, usually on the back. A common portable air source comprises a turbo unit, including a fan driven by a motor powered by a battery and a filter. The device is intended to provide a breathable air supply for a pre-determined period of time, typically four hours.
A problem with known respirator hoods is that the air duct is regularly made of soft, flexible material similar to the hood. As a result, the shape and volume cab be unstable, and local variations in the cross-section of the air duct can occur from day-to-day and from one hood to another. Variations in duct cross-section can restrict the air flow the user and, in extreme cases, the duct may even close to shut-off the air supply.
A reduced air flow may be insufficient to provide the user with an acceptable volume of breathable air and to flush exhaled air containing a higher carbon dioxide content from the hood. As a result, a build-up of carbon dioxide may occur, giving rise to potentially serious health and safety risks. For example, the user may become dizzy, feel claustrophobic, and eventually collapse. This can be a problem when the hoods are connected to a portable breathable air supply or a separate, remote air supply.
Variations in air duct cross-section can also increase the back pressure that, in turn, affects battery performance for the portable powered air supply. In particular, the turbo unit must work harder to overcome the higher back pressure, which requires more power and consumes battery life.
Another problem with known respirator hoods is that the duct air outlet directs the air supply onto the user's face, where the air-stream passes over the eyes before reaching the nose and mouth. As a result, the eyes tend to dry out and become uncomfortable. This problem can be exacerbated when the user wears spectacles that further channel the air stream into close contact with the eyes. The time the user can work before having to remove the hood can be reduced, causing increased work interruption with consequential lost time while the user moves to a safe environment.
Another problem with known respirator hoods is that they can provide areas where contaminants collect, which areas can be difficult or awkward to clean effectively. For example, the air supply line is often a corrugated hose that is permanently secured to the hood and cannot be easily cleaned in situ. This is a particular problem for hood use in a toxic environment where cleaning is performed at the end of each working day. The hood may become unusable and have to be thrown away although otherwise still in good condition.